Cillian Murphy says it takes him around a month to get his accent ready for Peaky Blinders.

The Cork actor plays Tommy Shelby, the leader of the Birmingham based criminal gang, and Cillian says he has to work hard to pull off the Birmingham accent ahead of filming.

“Every time I finish doing it (Peaky Blinders), I go 'I don’t know if I can do that again. I can’t conceive of how I did it in the first place',” he told The Dermot & Dave Show on Today FM.

“I might watch back the last episode of the last series to remind myself of the world but it’s a slow process.

“For me, it’s like taking your mouth to the gym. It takes about a month for me to figure an accent out. I’m not a good mimic.”

The fifth season of Peaky Blinders starts on BBC One this Sunday.

Cillian says the Shelby family are forced to regroup and work together in the upcoming series as their world is set to be thrown into turmoil by the 1929 financial crash.

He says it's a much different threat to those they have faced in the past.

“There’s an incident that happens at the very beginning of episode 1, that they (the Shelby family) have no choice but to all regroup and they only work well together in the face of adversity. They don’t really work well when things are going grand.

“The threat that they’re faced with this series is very different. Last year it was the Mafia and that’s a very tangible, visible threat but this year it’s kind of economic and ideological and for Tommy, psychological.

“In this series, you’ll see that Lizzie (played by Natasha O’Keeffe) becomes a real powerhouse and really challenges Tommy’s leadership. She stands up to him brilliantly.”